U.S. patent application number 11/472030 was filed with the patent office on 2007-01-18 for optical measuring system and optical measuring method.
This patent application is currently assigned to Carl Zeiss AG. Invention is credited to Christoph Hauger, Peter Reimer.
Application Number | 20070013918 11/472030 |
Document ID | / |
Family ID | 34706425 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070013918 |
Kind Code |
A1 |
Hauger; Christoph ; et
al. |
January 18, 2007 |
Optical measuring system and optical measuring method
Abstract
The invention provides an optical measuring system and an
optical measuring method, which are particularly useful for the
acquisition of image data of a retina of an eye. Data acquisition
is made by OCT measurements, wherein a quality of these measurement
is improved by arranging an active optical element in the beam
path.
Inventors: |
Hauger; Christoph; (Aalen,
DE) ; Reimer; Peter; (Ellwangen, DE) |
Correspondence
Address: |
POTOMAC PATENT GROUP, PLLC
P. O. BOX 270
FREDERICKSBURG
VA
22404
US
|
Assignee: |
Carl Zeiss AG
Oberkochen
DE
|
Family ID: |
34706425 |
Appl. No.: |
11/472030 |
Filed: |
June 21, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP04/14636 |
Dec 22, 2004 |
|
|
|
11472030 |
Jun 21, 2006 |
|
|
|
Current U.S.
Class: |
356/512 ;
356/497 |
Current CPC
Class: |
A61B 3/1015 20130101;
A61B 3/1005 20130101; G01N 21/47 20130101; A61B 3/12 20130101; A61B
3/102 20130101; G01J 9/00 20130101 |
Class at
Publication: |
356/512 ;
356/497 |
International
Class: |
G01B 11/02 20060101
G01B011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2003 |
DE |
103 60 570.3 |
Claims
1. An optical measuring system, comprising: at least one radiation
source; a first beam splitter; a second beam splitter; an OCT
detector; a wavefront detector; at least one active optical
element; and a collimator; wherein the radiation source, the first
beam splitter, the second beam splitter, the OCT detector, the
wavefront detector, the at least one active optical element, and
the collimator are arranged such that a source beam generated by
the at least one radiation source is divided into an object
illuminating beam and a reference beam by the first beam splitter;
the object illuminating beam is directed by the collimator to an
object position via the at least one active optical element;
radiation emanating from the object position is formed to an object
measuring beam by at least the collimator; the object measuring
beam is directed to the second beam splitter via the at least one
active optical element; the object measuring beam is divided into
an OCT measuring beam and a wavefront measuring beam by the second
beam splitter; the wavefront measuring beam is directed to the
wavefront detector; the OCT measuring beam is directed to the OCT
detector; and the reference beam is directed to the OCT
detector.
2. The optical measuring system according to claim 1, further
comprising a control adapted for controlling the at least one
active optical element in dependence of a measurement signal
provided by the wavefront detector.
3. The optical measuring system according to claim 1, further
comprising a control adapted for controlling the at least one
active optical element in dependence of a measurement signal
provided by the wavefront detector such that wavefronts of the
wavefront measuring beam at the wavefront detector are
substantially plane wavefronts.
4. The optical measuring system according to claim 1, wherein the
active optical element is adapted to alter an optical path length
of a beam directed via the active optical element between an input
cross section before interaction of the beam with the active
optical element, and an output cross section after the interaction
of the beam with the active optical element, position-dependent
across the output cross section.
5. The optical measuring system according to claim 1, further
comprising at least a first scanner for altering the object
position.
6. The optical measuring system according to claim 1, further
comprising a second scanner for changing an optical path length of
the reference beam between the first beam splitter and the OCT
detector.
7. The optical measuring system according to claim 1, wherein the
wavefront sensor comprises a Hartmann-Shack sensor.
8. The optical measuring system according to claim 1, wherein the
OCT detector comprises a line detector.
9. The optical measuring system according to claim 1, wherein a
refractive power of the collimator is variable, and the control is
adapted to control the refractive power of the collimator in
dependence of a measurement signal provided by the OCT
detector.
10. An optical measuring method, comprising: performing at least
one OCT measurement on an object to be examined, by generating
object illuminating light; sending a first portion of the object
illuminating light to the object; and superposing at least a first
portion of object measurement light emanating from the object with
a second portion of the object illuminating light; performing at
least one wavefront measurement on at least a second portion of the
object measurement light emanating from the object; changing
optical path lengths of a beam formed by the object illuminating
light between the generation of the object illuminating light and
the object, wherein the optical path lengths are changed depending
on a position across a cross section of the beam and based on the
at least one wavefront measurement; and changing optical path
lengths of a second beam formed by the object measurement light
between the object and the superposition of the object measurement
light wherein the optical path lengths are changed depending on a
position across a cross section of the beam and based on the at
least one wavefront measurement.
11. The optical measuring method of claim 10, wherein a region of
the first beam and a region of the second beam overlap.
12. The optical measuring method of claim 11, wherein the changing
of the optical path length of the first beam and the changing of
the optical path length of the second beam is performed by an
active optical element positioned in the region of the first beam
where same overlaps with the second beam.
13. The optical measuring method of claim 10, further comprising
focussing the object measurement light in a first region of the
object.
14. The optical measuring method of claim 13, further comprising
moving the first region in a direction of a direction of incidence
of the object measurement light on the object.
15. The optical measuring method of claim 13, further comprising
moving the first region in a direction transverse to a direction of
incidence of the object measurement light on the object.
16. The optical measuring method of claim 13, further comprising
focussing the object illuminating light to a plurality of
adjacently arranged different first regions, and performing for
each of the plurality of first regions the at least one OCT
measurement, without changing the optical path lengths of the first
and second beam, after performing the at least one wavefront
measurement and changing the optical path lengths of the first and
second beams based on the at least one wavefront measurement.
17. The optical measuring method of claim 16, wherein the plurality
of adjacently arranged different first regions are arranged within
a second contiguous region of the object, wherein the second region
is larger than the first regions.
18. The optical measuring method of claim 17, wherein the at least
one wavefront measurement and the focussing to the first regions
are repeatedly performed for a plurality of the second contiguous
regions which mutually overlap at most partially.
19. The optical measuring method of claim 16, further comprising
moving the first region in a direction of a direction of incidence
of the object measurement light on the object, wherein the moving
of the first region in the direction of incidence is made before
performing the at least one wavefront measurement and is
substantially not made between focussings of the object
illuminating light to the different first regions.
20. The optical measuring system according to claim 1, wherein the
at least one radiation source comprises separate light sources
differing with respect to their wavelengths.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Present invention relates to an optical measuring system and
an optical measuring method.
[0003] In particular, the measuring system and the measuring method
can be used for examining a retina of an eye of a patient, and for
creating a data set, from which images of the retina can be
created. The data set can, in particular, be two-dimensional or
three-dimensional.
[0004] 2. Brief Description of Related Art
[0005] From U.S. Pat. No. 5,321,501, an optical measuring system
for the examination of a retina of an eye is known. The disclosure
of this document is fully incorporated by reference into the
present application.
[0006] From pages 29 and 30 of the Program Year 2 of the Annual
Report of the National Science Foundation, Center for Adaptive
Optics, University of California, Santa Cruz, Calif., a retina
camera is known, which is subsequently discussed in conjunction
with FIG. 1.
[0007] The camera 1 serves to take images of a retina 3 of an eye 5
of a patient. The camera 1 operates according to an OCT-method,
wherein OCT stands for "Optical Coherence Tomography". Two light
sources 7 and 9 are provided for selectively or together creating a
source beam 11, which is divided into an object illuminating beam
15 and a reference beam 17 by a first beam splitter 13. The
reference beam 17 is reflected back into itself at an
actuator-mirror-unit 19, wherein an optical path length of the
reference beam between the beam splitter 13 and its reflection at
the actuator-mirror-unit 19 is variable via an actuator of the unit
19. The object illuminating beam 15 is focussed onto the retina 3
by a lens 21 of the eye 5, and light of the object illuminating
beam reflected or scattered back from the retina 3 is again
incident on the beam splitter 13 and is transmitted therethrough.
The light of the reference beam reflected off the
actuator-mirror-unit 19 is reflected at the beam splitter 13 and is
superimposed with the light coming back from the retina, to form a
common light beam 22. The light beam 22 is directed via lenses 25
to an active optical element 27 and reflected therefrom. The
reflected beam 22 is directed via a further lens 29 and a mirror 30
to a second beam splitter 33. The beam splitter 33 divides beam 22
into an OCT measuring beam 35 and a wavefront measuring beam 37.
The OCT measuring beam 35 is directed via lenses 39 onto a camera
49, which obtains OCT measuring data from a depth of the retina 3
set by actuating the actuator-mirror-unit 19.
[0008] The wavefront measuring beam 37 is directed to a
Hartmann-Shack wavefront sensor 41 via a lens 39, to detect
wavefronts in the beam 22. The active optical element 27 is
actuated in dependence of the detected wavefronts in order to
improve on a quality of the OCT images obtained by the detector
49.
[0009] It has been found that this conventional system does not
fulfill expectations with regard to its imaging quality, in
particular with respect to its lateral and depth resolution.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide an optical measuring system and an optical measuring
method, in particular for measuring a retina of an eye, which
compared to the conventional measuring system has an improved
imaging quality.
[0011] Under a first aspect, the invention provides an optical
measuring system, which comprises a radiation source, a first beam
splitter, a second beam splitter, an OCT detector, a wavefront
detector, at least one active optical element and a collimator.
These components are arranged into an optical circuitry in such a
manner, that a source beam to be generated by the radiation source
is divided by the first beam splitter into an object illuminating
beam and a reference beam; the object illuminating beam is directed
via the at least one active optical element through the collimator
to an object position, radiation emanating from the object position
is formed by the collimator into an object measurement beam; the
object measurement beam is directed via the at least one active
optical element to the second beam splitter; the object measurement
beam is divided into an OCT measurement beam and a wavefront
measurement beam by the second beam splitter; the wavefront
measurement beam is directed to the wavefront detector; the OCT
measurement beam is directed to the OCT detector; and the reference
beam is directed to the OCT detector.
[0012] In the measuring system according to the invention, the at
least one active optical element may be controlled in dependence of
a measurement signal provided by the wavefront detector, to improve
on a quality of the measurement signal provided by the OCT
detector. This results in an improvement on the data obtained from
the object by the system. Herein, and in contrast to the
conventional system, both the object measurement beam and the
wavefront measurement beam are directed via the active optical
element, whereas the light of the reference beam is not directed
via the active optical element in its path to the OCT detector.
Such an active optical element is commonly termed an adaptive
optical element, and optics containing such an element are termed
adaptive optics.
[0013] According to a preferred embodiment, the active optical
element is set such that the wavefronts detected by the wavefront
detector are substantially planar wavefronts.
[0014] The active optical element has an extended cross section,
within which the beam directed via the active optical element
interacts with same. Herein, the active optical element is adapted
to provide for the beam variable optical path lengths
position-dependent within the cross section.
[0015] The active optical element may operate in reflection, i.e.
it reflects the beam directed to it, or in transmission, i.e. it
transmits the beam directed through it.
[0016] According to an exemplary embodiment a first scanner is
provided, to move a position at which the object illuminating beam
is incident on the object, in a direction transverse to the
direction of the incident object illuminating beam. Herein, the
first scanner may be pivotable in two directions in order to allow
for two-dimensional scanning of the object.
[0017] According to an exemplary embodiment, the active optical
element is used as the first scanner.
[0018] According to a further exemplary embodiment a second scanner
is provided, for changing an optical path length of the reference
beam between the first beam splitter and the OCT detector. Thereby,
the object can be scanned according to the OCT method in its depth,
i.e. in the direction of the incident object illuminating beam.
[0019] According to an exemplary embodiment, the wavefront sensor
is a Hartmann sensor or a Hartmann-Shack sensor.
[0020] According to a further exemplary embodiment, the object
position, i.e. the position at which the object illuminating beam
is focussed in the object, can also be moved in the beam direction
of the illuminating beam, for moving that region of the object,
from which OCT data are acquired, in the depth direction of the
object.
[0021] According to an exemplary embodiment, to achieve this the
collimator is variable, for example by translation in the direction
of the object illuminating beam.
[0022] According to a further exemplary embodiment, the at least
one active optical element is controlled to having a focussing or
defocussing effect on the illuminating light beam.
[0023] According to a further aspect of the invention, there is
provided an optical measuring method, comprising performing at
least one OCT measurement on an object to be examined, and
performing at least one wavefront measurement. The OCT measurement
is made by generating object illuminating light, sending a first
portion of the object illuminating light to the object, and
interferingly superimposing at least portion of object measurement
light emanating from the object with a second portion of the object
illuminating light. Performing the at least one wavefront
measurement is made with at least a portion of the measurement
light emanating from the object.
[0024] Furthermore, to improve on a quality of the performed
measurement, optical path lengths of a beam formed by the object
illuminating light between its generation and the object are
changed, wherein this change is made position-dependent across a
cross section of the beam and in dependence of the at least one
wavefront measurement. Similarly, optical path lengths of a second
beam formed by the object measurement light between the object and
the interferent superposition are changed.
[0025] According to an exemplary embodiment, first the at least one
wavefront measurement is performed, and in dependence thereof, a
setting of the optical path lengths of the first and second beam is
performed. Then, a plurality of OCT measurements is carried out, in
each of which the object illuminating light is focussed at a
different small region of the object. Thereby, OCT measurement data
can quickly be obtained from an extended region of the object, at
an unchanged setting of the optical path lengths of the first and
second beam.
[0026] According to a further exemplary embodiment, it is envisaged
to move a window in which measurement data is acquired, laterally
to a propagation direction of the object illuminating light, after
acquisition of measurement data in said window, and to anew acquire
OCT measurement data in the moved window, but to beforehand perform
a further wavefront measurement for carrying out suitable settings
of the optical path lengths of the first and second beam for the
moved window.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In the following, exemplary embodiments of the present
invention are explained in further details with reference to the
figures, wherein
[0028] FIG. 1 shows an arrangement of a conventional optical
measuring system;
[0029] FIG. 2 shows an arrangement of an optical measuring system
according to an embodiment of the invention;
[0030] FIG. 3 shows schematically an explanation of an optical
measuring method according to an embodiment of the invention;
and
[0031] FIG. 4 shows a further embodiment of an optical measuring
system according to the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0032] In FIG. 2, an embodiment of an optical measurement system
according to the present invention is shown as a circuit scheme of
an optical circuit of same.
[0033] The optical measurement system la comprises a radiation
source 9a for generating a source beam 11a via collimating lenses
51 and a space filter 52. Herein, the radiation source 9a is a
radiation source suitable to generate light with which an OCT
measurement method can be performed on an object to be examined. In
particular, this light is temporally incoherent, and may further
also be spatially incoherent. For example, the radiation source 9a
may for this purpose be a superluminescence diode. The object to be
examined may be, for example, a retain 3a of an eye 5a of a
patient.
[0034] Through a first beam splitter 13a, the source beam 11a is
divided into a reference beam 17a and an object illuminating beam
15a. The reference beam 17a is reflected at a mirror 53 of an
actuator-reflector-unit 19a, and is reflected onto itself,
reflected at the first beam splitter 13a and directed onto an OCT
detector 49a via a lens 39a, a confocal aperture 76 and a further
lens 40. The unit 19a further comprises an actuator 55 for moving
the mirror 53 relative to a basis 57, so that an optical path
length of the reference beam 17a between its division at the beam
splitter 13a and the mirror 53 is variable.
[0035] The object illuminating beam 15a passes through a second
beam splitter 33a and is directed via lenses 25a to an active
optical element 27a reflecting the object illuminating beam 15a. An
example for such an active optical element is a deformable mirror
as can be obtained from the company Xinetics, Inc., 37 MacArthur
Ave., Devens, MA 01432, USA. The object illuminating beam 15a,
where incident on the active optical element 27a, has an extended
cross section, and the active optical element 27a is controllable
via a control line 59 from the control 61, to locally deform a
mirror surface provided by the active optical element 27a for the
incident beam 15a.
[0036] After reflection off the active optical element 27a, the
object illuminating beam 15a passes through one or more lenses 29a
and is incident on a scanning mirror 63, is reflected by same,
passes through a further lens optics 65, and, after reflection at a
further mirror 67, enters into an eye 5a through the lens 21a of
the eye 5a in such a manner, that the object illuminating beam 15a
is incident on the retina 3a of the eye 5a at an object position
69. The scanning mirror 63 is controllable to two-dimensionally
move the object position 69 transversely to a direction of
incidence of the object illuminating beam 15a on the retina 3a.
[0037] Radiation emanating from the retina 3a at the object
position 69 is formed by the eye lens 21a to an object measurement
beam 73, the principal axis 74 of which substantially coincides
with a principal axis 72 of the object illuminating beam 15a, so
that the object measurement beam 73 is directed back to the beam
splitter 33a via the mirror 67, the lens 65, the pivoting mirror
63, the lens 29a, the active optical element 27a and the lenses
25a. By the beam splitter 33a, the object measurement beam 73 is
divided into an OCT measurement beam 75 and a wavefront measurement
beam 77. The OCT measurement beam 75 passes through the beam
splitter 13a and thereby interferingly overlaps with the reference
beam 17a, so that the OCT detector 49a registers an OCT measurement
signal, which is transmitted to the control 61 via a line 78.
[0038] The wavefront measurement beam 77 enters into the wavefront
detector 41a, which is provided by a Hartmann sensor or a
Hartmann-Shack sensor, for example. There, the wavefront
measurement beam 77 is divided into a manifold of partial beams 81
by an array 79 of microlenses, wherein each partial beam 81 is
focussed onto a spatially resolving detector 83. Via a line 85, an
image of the detector 83 is transmitted to the control 61, which
evaluates focus positions of the partial beams 81 in the detector
image and, in dependence of the evaluation, controls the active
optical element 27a in such a manner that wavefronts in the
wavefront measurement beam 77, and therefore also in the object
measurement beam 73, are substantially planar wavefronts. Thereby,
wavefront aberrations due to non-perfect imaging of, e.g., the lens
21a of the eye 5a, or/and due to irregularities in the vitrious
body of the eye, or/and due to a non-perfect imaging of the
measuring optics in the object measurement beam 73, are
compensated, so that the OCT measurement beam 75 is prepared such
that its wavefronts can almost ideally interfere with wavefronts of
the reference beam 17a, so that the OCT measurement signal provides
a particularly good depth resolution and lateral resolution of the
retina. Herein, the optical path length between the beam splitter
13a and the mirror 53 substantially corresponds to the optical path
length of the object measurement beam between the object position
69 and the beam splitter 13a. Thereby, a depth resolution of, e.g.,
1 .mu.m to 5 .mu.m can be achieved.
[0039] At the same time, wavefronts of the object illuminating beam
15a are prepared by so controlling the active optical element, in
such a manner that in the presence of the irregularities of the
virtious body and the non-perfect imaging of the eye lens 21a, a
particularly small spot on the retina 3a is illuminated at the
object position 69, so that also the lateral resolution of the
measurement data provided by the measuring system 1a is of a high
quality. Thereby, it is possible to achieve a lateral resolution
of, e.g., 1 .mu.m to 10 .mu.m.
[0040] An OCT measurement is performed at an object position 69,
through the control 61 activating via a control line 87 the
actuator 55, so that same moves the mirror 53 in a certain range,
i.e. by a certain displacement, to change the optical path length
of the reference beam 17a between the beam splitter 13a and the OCT
detector 49a in a range corresponding to twice the displacement.
During such a displacement, the control 61 reads out plural
measurement values of the OCT detector 49a, wherein these
measurement values correspond to detected intensities.
[0041] In conjunction with FIG. 3, in the following a method for
obtaining three-dimensional measurement data from a volume portion
93 of the retina 3a is described.
[0042] The volume portion 93 in FIG. 3 is confined on top by a
surface 91 of the retina, and extends over a length of 5 mm in
x-direction and 5 mm in y-direction, wherein the x-direction and
the y-direction extend transversely to the direction of the object
illuminating beam 15a incident on the retina 3a. In a z-direction
orthogonal to the x-direction and the y-direction, the volume
portion 93 extends over 500 .mu.m into the depth of the retina
3a.
[0043] With the method as described, measurement data from three
different depths (in z-direction) are acquired. These layers are
labelled 95.sub.1, 95.sub.2 and 95.sub.3, respectively, in FIG. 3.
Each of these layers is divided in xy-direction into, e.g., eight
fields or windows. Initially, the object position is moved to the
center of field #1, by controlling pivoting mirror 63 and by
controlling the active optical element 27a in such a manner that
same provides a focussing or defocussing effect such that the focus
of the object illuminating beam 15a is in the plane 951 of the
retina 3a. Then, the control 61 evaluates an image of the wavefront
sensor 41a and thereafter sets the active optical element 27a in
such a manner that the wavefronts in the OCT measurement beam 75
are substantially planar wavefronts. After this setting, the
pivoting mirror 63 is controlled in such a manner that the object
position 69 is sequentially located at, e.g., 25 different
positions within the window #1, the 25 positions being arranged in
a 5-by-5-grid. At each of the 25 positions, the object position is
maintained for a time within which the actuator 55, controlled by
the control 61, can perform at least one displacement, to carry out
an OCT measurement with the OCT detector 49a. Thereby, within
window #1 25 OCT measurement data sets are obtained.
[0044] Then, the object position is moved to the center of field #2
in plane 95.sub.2, by accordingly setting the pivoting mirror 69
and the focussing or defocussing effect of the active optical
element 27a as described above, wherein also the actuator 55 is
controlled to adapt the optical path length of the reference beam
to the position of the plane 95.sub.2. Again, a wavefront
measurement is carried out, for setting the active optical element
such that for the center of window #2, the wavefronts in the OCT
measurement beam 75 are substantially planar wavefronts. Then,
another 25 OCT measurements are performed within the window #2.
[0045] Thereafter, corresponding measurements are carried out
sequentially for fields #3 and #4 in plane 95.sub.3, field #5 in
plane 95.sub.2, fields #6 and #7 in plane 95.sub.1, and so on.
[0046] In this manner, the measurement data for the three planes
95.sub.1, 95.sub.2 and 95.sub.3 can quickly be obtained. Herein,
the settings of the active optical element 27a are the same for the
different positions within one window, but may be different from
window to window within one of the planes 95. Herein, the size of
the windows can be adapted in accordance with the required accuracy
to be achieved, with regard to a fast scanning of all the
measurement positions within the planes.
[0047] Alternatively, it is also possible to first scan all the
windows within one of the planes, and to then switch to the next
plane. In the example shown in FIG. 3, the windows may be scanned
in the following sequence: #1, #24, #19, #6, #7, #18, #13, #12;
#11, #14, #17, #8, #5, #20, #23, #2; #3, #22, #21, #4, #16, #9,
#10, #15.
[0048] In the following, variants of the embodiments described in
conjunction with FIGS. 2 and 3 are explained. Components which
correspond to one another with respect to their function and/or
structure are labelled by corresponding numerals, which are
supplemented by additional letters for discrimination.
[0049] An optical measuring system as shown in FIG. 4 has a similar
setup as the measuring system shown in FIG. 2.
[0050] An essential difference between the two measuring systems
lies in the detection of the OCT measurement signal. Namely, in the
measuring system 1b of FIG. 4, a source beam 11b generated by a
radiation source 9b is divided by a beam splitter 13b into an
object illuminating beam 15b and a reference beam 17b. A beam path
of the object illuminating beam 15b between the beam splitter 13b
and a retina 3b of an eye 5b is similar to the beam path shown in
FIG. 2, as well as a beam path of the light emanating from the
retina 3b back to the beam splitter 13b as an object measurement
beam 75b. The object measurement beam 75b passes through the beam
splitter 13b and is coupled into a glass fiber 101 by a collimating
lens 39b, and is directed by the glass fiber 101 to a radiation
exit 103, from which the light of the beam 75b is emitted onto a
line detector 49b.
[0051] The reference beam 17b is coupled by a collimator 105 into a
glass fiber 107, directed through a fiber coupler 109, further
directed by a glass fiber 111 and emitted from the same at a fiber
end 113. The emitted light is collimated by a collimator 115 and
reflected at a mirror 53b. A distance of the mirror 53b from the
fiber end 103 is variable by an actuator 55b, which is controlled
via a line 87b. The light reflected at the mirror 53b is then
coupled back into the end 103 of the fiber 111 by the collimator
115, and travels back to the fiber coupler 109, where part of its
intensity is coupled into a fiber 117, from where it is emitted at
a fiber end 119 towards the line detector 49b.
[0052] The two fiber ends 103 and 119 are spaced apart by a
distance, so that at one site of the line detector, the optical
path length in the beam path between beam splitter 13b, mirror 53b,
fiber end 119 and the site on the line detector 49b is equal to the
optical path length between the beam splitter 13b, via the active
optical element 27b to a certain depth of the retina 3b, back via
the active optical element 27b and via the end 103 of the fiber 101
to the said site on the line detector 49b, so that at this site,
the interference condition is fulfilled for the respective depth of
the retina. At a different site on the line detector 49b, the
interference condition is fulfilled for a different depth of the
retina 3b, so that by means of the line detector, a plurality of
measurement data can be obtained simultaneously, whereby a
particularly fast scanning of the retina 3b can be accomplished.
This plurality of measurement data corresponds to the plurality of
measurement data acquired in the embodiment of FIG. 2 via a
displacement of the actuator.
[0053] Herein, it is also possible to provide a variable spacing
between the fiber ends 103 and 119, e.g. by a drive or an actuator.
By changing the distance between the fiber ends, it is then
possible to change the depth range simultaneously detectable by the
line detector. At a larger spacing between the fiber ends, this
depth range is larger than at a smaller spacing. For example, the
spacing between the fiber ends 103, 119 can be set to cover, with
reference to FIG. 3, the entire depth range of the retina at once,
so that in addition to the planes 95.sub.1, 95.sub.2 and 95.sub.3
also regions between these planes are detected. Thereby, the entire
depth of the retina or part of it can be scanned, without making
changes in the optical path length of the reference beam. It may;
however, be advantageous in this case to set the focussing of the
object illuminating beam to one of the planes 95.sub.1, 95.sub.2
and 95.sub.3, and to carry out the scanning of the various windows
in this plane with such a focus setting. Then, the beam may be
focussed to a different plane, followed by scanning of this plane.
Because those planes, to which the focus has not been set, are not
detected with the best attainable quality, it is possible, in order
to speed up measurement, not to read out the data associated with
these planes, and to restrict reading out the line detector to
detector regions onto which structures of the retina are imaged, to
which the object illuminating beam has been focussed.
[0054] In the embodiments described above, a single active optical
element is used to change optical path lengths within the object
illuminating beam and within the object measurement beam.
[0055] However, it is also possible to separate the object
illuminating beam from the object measurement beam, and to direct
both beams via separate, accordingly controlled active optical
elements.
[0056] In the embodiments described above, a single light source is
used to generate the light for the OCT measurement and the
wavefront measurement. However, it is also possible to use separate
light sources, which differ for example with respect to their
wavelengths. The light of the two light sources may then be
superposed to a common object illuminating beam.
[0057] In the embodiments described above, the beam splitter for
coupling the wavefront measurement beam out of the object
measurement beam is arranged in same in front of the beam splitter
for dividing the beam into the object illuminating beam and the
reference beam. However, it is also possible to alter the ordering
of the beam splitters in the object measurement beam.
[0058] In the embodiments described above, a single pivoting mirror
is provided to move the object position laterally to the direction
of the object illuminating beam. However, it is also possible to
use two separate mirrors, which allow for independently moving the
object position in one direction each. Herein, it is also possible
to provide the function of the one pivoting mirror or the other
pivoting mirror by the active optical element, which is possible by
accordingly controlling the active optical element.
[0059] In the embodiments described above, the focus setting of the
object illuminating beam to a depth of the retina is effected by an
according controlling of the active optical element. However, it is
also possible to actuate other beam forming elements of the object
illuminating beam for this purpose, for example by moving such
elements along the direction of the object illuminating beam.
[0060] It is also envisaged to use for this purpose optical
elements whose optical properties are variable by applying a
control signal. An example therefore are electrically variable
lenses as obtainable from, e.g., the company Varioptic, 69007 Lyon,
France.
[0061] While the invention has been described also with respect to
certain specific embodiments thereof, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, the exemplary embodiments of
the invention set forth herein are intended to be illustrative and
not limiting in any way. Various changes may be made without
departing from the spirit and scope of the present invention as
defined in the following claims.
[0062] The invention provides an optical measuring system and an
optical measuring method, which are particularly useful for the
acquisition of image data of a retina of an eye. Data acquisition
is made by OCT measurements, wherein a quality of these measurement
is improved by arranging an active optical element in the beam
path.
* * * * *